A week ago, I was one of the winners of the Internet of Useful Things Hackaday 2017 Contest! It is an honor to be selected. I was even written up in the in a HACKADAY.IO BITS....

We've found useful Internet of Things things

By Brian Benchoff

To our shock and amazement, the Internet of Things can be useful, and it's more than just tweeting toasters and Internet-connected spy cameras. Check out the winners of the Internet of Useful Things phase of the Hackaday Prize which we announced yesterday.

Just look at entries like the iDONT -- the Internet Doorbell On/Off Trigger. This is a project to connect your doorbell to the Internet, giving you the ability to turn the doorbell off for meals and naps, and send doorbell push notifications to your phone. [David Spinded] created this device with a relay and an ESP32 microcontroller. It's so simple and so brilliant we're shocked this isn't a commercial product yet.

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Thanks Brian for describing my project better than I did!

Enough celebrating....get back to work....

One thing that I have been struggling with is what relay to use. I have been running into an issue with the relays freezing up and I think I know why now. I have been using two relays (one for the line and one for the neutral) and controlling them with two different microcontroller pins. While in the code, the command to change the IO state happens one after another, it is not instant. I am thinking now that the relays were freezing because half of the doorbell was on AC and half on DC for long enough that the load side of the relays were seeing some "crazy" things and not switching.

By using the same microcontroller IO the relays will be switched at the same time. To address the 12mA drive limit of the ESP32 a transistor will be used off the IO to switch the relays.

So, I believe now that I can use relays that are inexpensive and widely available, for example the Songle SRD-05VDC-SL-C. These relays are in so many relay modules that are under $5 on ebay, or in piece parts for under $0.25 with free shipping. This certainly beats paying ~$10 for a high power SSR. While I have done a bit of testing of this, I need to completely prove this out.

Until next time, happy hacking.